Tuesday, April 6, 2010

Exotic antimatter detected at Relativistic Heavy Ion Collider (RHIC)

Scientists report discovery of heaviest known antinucleus and first antinucleus containing an anti-strange quark, laying the first stake in a new frontier of physics

This diagram is known as the 3-D chart of the nuclides. The familiar Periodic Table arranges the elements according to their atomic number, Z, which determines the chemical properties of each element. The vertical axis represents strangeness, S, which is zero for all naturally occurring matter, but could be non-zero in the core of collapsed stars. Antinuclei lie at negative Z and N in the above chart, and the newly discovered antinucleus (magenta) extends the 3-D chart into the region of strange antimatter.

UPTON, NY — An international team of scientists studying high-energy collisions of gold ions at the Relativistic Heavy Ion Collider (RHIC), a 2.4-mile-circumference particle accelerator located at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, has published evidence of the most massive antinucleus discovered to date. The new antinucleus, discovered at RHIC’s STAR detector, is a negatively charged state of antimatter containing an antiproton, an antineutron, and an anti-Lambda particle. It is also the first antinucleus containing an anti-strange quark. The results will be published online by Science Express on March 4, 2010.

“This experimental discovery may have unprecedented consequences for our view of the world,” commented theoretical physicist Horst Stoecker, Vice President of the Helmholtz Association of German National Laboratories. “This antimatter pushes open the door to new dimensions in the nuclear chart — an idea that just a few years ago, would have been viewed as impossible.”

The discovery may help elucidate models of neutron stars and opens up exploration of fundamental asymmetries in the early universe.

All terrestrial nuclei are made of protons and neutrons (which in turn contain only up and down quarks). The standard Periodic Table of Elements is arranged according to the number of protons, which determine each element’s chemical properties. Physicists use a more complex, three-dimensional chart to also convey information on the number of neutrons, which may change in different isotopes of the same element, and a quantum number known as “strangeness,” which depends on the presence of strange quarks (see diagram). Nuclei containing one or more strange quarks are called hypernuclei.

For all ordinary matter, with no strange quarks, the strangeness value is zero and the chart is flat. Hypernuclei appear above the plane of the chart. The new discovery of strange antimatter with an antistrange quark (an antihypernucleus) marks the first entry below the plane. …

Exotic Antimatter Detected at Relativistic Heavy Ion Collider (RHIC)

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